Peripheral Nervous System 2:The Autonomic System

Lawrence M. Witmer, PhDProfessor of Anatomy

Dept. of Biomedical SciencesHeritage College of Osteopathic

Medicine, Ohio UniversityAthens, Ohio 45701witmerL@ohio.edu

Handout download: Blackboard orhttp://www.oucom.ohiou.edu/

dbms-witmer/anatomy_immersion.htm

30 July 2012

Reading: Moore’s ECA4 36–43

Somatic vs. Visceralattribute Somatic System Visceral System

embryological origin of tissue

“body wall:” somatic (parietal) mesoderm (dermatome,

myotome)

“organs:” splanchnic (visceral) mesoderm,

endoderm

examples of adult tissues

dermis of skin, skeletal muscles, connective tissues

glands, cardiac muscle, smooth muscle

perception conscious, voluntary unconscious, involuntary

Langman’s Embryo 9 2004

Sensory/Motor + Somatic/Visceral

Somatic VisceralSensory

(Afferent)somatic sensory[General Somatic Afferent (GSA)]

visceral sensory[General Visceral Afferent (GVA)]

Motor(Efferent)

somatic motor[General Somatic Efferent (GSE)]

visceral motor[General Visceral Efferent (GVE)]

SomaticNervousSystem

AutonomicNervousSystem

(July 16) (today)

Overview of the Autonomic Nervous SystemSimilarities between Sympathetic & Parasympathetic

• Both are efferent (motor) systems: “visceromotor”• Both involve regulation of the “internal” environment generally

outside of our conscious control: “autonomous”• Both involve 2 neurons that synapse in a peripheral ganglion• Innervate glands, smooth muscle, cardiac muscle

CNS ganglion

preganglionicneuron

postganglionicneuron

glands

smoothmuscle

cardiacmuscle

Overview of the Autonomic Nervous SystemDifferences between Sympathetic & Parasympathetic

Location of Preganglionic Cell Bodies

ThoracolumbarT1 – L2/L3 levels of the spinal cord

CraniosacralBrain: CN III, VII, IX, XSpinal cord: S2 – S4

Sympathetic Parasympathetic

SympatheticCNS ganglion

short preganglionicneuron

long postganglionicneuron

target

ParasympatheticCNS ganglion

long preganglionicneuron

target

short postganglionicneuron

Overview of the Autonomic Nervous SystemDifferences between Sympathetic & Parasympathetic

Relative Lengths of Neurons

Parasympathetic

Overview of the Autonomic Nervous SystemDifferences between Sympathetic & Parasympathetic

Neurotransmitters

ACh, +

NE (ACh at sweat glands),+ / -, α & ß receptors

ACh, + / -muscarinic receptors

• All preganglionics release acetylcholine (ACh) & are excitatory (+)• Symp. postgangl. — norepinephrine (NE) & are excitatory (+) or inhibitory (-)• Parasymp. postgangl. — ACh & are excitatory (+) or inhibitory (-)

Sympathetic

• Excitation or inhibition is a receptor-dependent & receptor-mediated response

Potential for pharmacologicmodulation of autonomic responses

ACh, +

Overview of the Autonomic Nervous SystemDifferences between Sympathetic & Parasympathetic

Target TissuesParasympatheticSympathetic

• Organs of head, neck, trunk, & external genitalia

• Organs of head, neck, trunk, & external genitalia

• Adrenal medulla• Sweat glands in skin• Arrector muscles of hair• ALL vascular smooth muscle

» Sympathetic system is distributed to essentially all tissues (because of vascular smooth muscle)

» Parasympathetic system never reaches limbs or body wall (except for external genitalia)

Overview of ANSFunctional Differences

Sympathetic• “Fight or flight”• Catabolic (expend energy)

Parasympathetic• “Feed & breed”, “rest &

digest”• Homeostasis

» Dual innervation of many organs — having a brake and an accelerator provides more control

Structure of spinal nerves: Somatic pathways

dorsal rootdorsal rootganglion

ventral root

spinalnerve

dorsalramus

ventralramus

dorsalhorn

ventralhorn

somaticsensory

nerve(GSA)

somaticmotornerve(GSE)

CNSinter-

neuron

Mixed SpinalNerve

gray ramuscommunicans white ramus

communicans

sympatheticganglion

spinalnerve

dorsalramus

ventralramus

gray ramuscommunicans white ramus

communicans

sympatheticganglion

intermediolateralgray column

Structure of spinal nerves: Sympathetic pathways

Moore’s COA6 2010

somatic tissues(body wall, limbs)

visceral tissues(organs)

Sympathetic System: Preganglionic Cell Bodies• Preganglionic cell bodies in

intermediolateral gray• T1 – L2/L3• Somatotopic organization

intermediolateralgray columns

lateralhorn

T1 –L2/L3

Clinical Relevance» dysfunction due to cord injury» spinal nerve impingement & OMM» referred pain

Sympathetic System: Postganglionic Cell Bodies

Paravertebralganglia

Prevertebral ganglia

• celiac ganglion• sup. mesent. g.• inf. mesent. g.

aorta

sympathetictrunk (chain)

1. Paravertebral ganglia• Located along sides of vertebrae• United by preganglionics into Sympathetic Trunk• Preganglionic neurons are thoracolumbar (T1–L2/L3)

but postganglionic neurons are cervical to coccyx• Some preganglionics ascend or descend in trunk

synapse atsame level

ascend tosynapse athigher level

descend tosynapse atlower level

Moore’s COA6 2010

Sympathetic System: Postganglionic Cell Bodies

Paravertebralganglia

Prevertebral ganglia

• celiac ganglion• sup. mesent. g.• inf. mesent. g.

aorta

sympathetictrunk (chain)

2. Prevertebral (preaortic) ganglia• Located anterior to abdominal aorta, in plexuses

surrounding its major branches• Preganglionics reach prevertebral ganglia via abdominopelvic splanchnic nerves

Moore’s COA6 2010

abdominopelvicsplanchnic

nerve

Sympathetic System: Summary

Moore’s COA6 2010

T1

L2

somatic tissues(body wall, limbs)

visceral tissues(organs)

postganglionicsvia 31 spinal

nervesto somatic tissues of neck, body wall,

and limbs

sympathetictrunk

prevertebralganglia

Cardiopulmonary Splanchnics: postganglionic fibers to thoracic

viscera

Abdominopelvic Splanchnics: preganglionic fibers to prevertebral ganglia,

postganglionic fibers to abdominopelvic viscera

ParasympatheticPathways

Moore’s COA6 2010

Cranial outflow• CN III, VII, IX, X• Four ganglia in head• Vagus nerve (CN X) is major

preganglionic parasymp. supply to thorax & abdomen

• Synapse in ganglia within wall of the target organs (e.g., enteric plexus of GI tract)

Sacral outflow• S2–S4 via pelvic splanchnics• Hindgut, pelvic viscera, and

external genitalia

Clinical Relevance» Surgery for colorectal cancer

puts pelvic splanchnics at risk» Damage causes bladder &

sexual dysfunction

Visceral Afferents and Referred Pain

Somatic sensation:• conscious, sharp, well-localized• touch, pain, temperature, pressure, proprioception

Visceral sensation:• often unconscious; if conscious: dull, poorly-localized• distension, blood gas, blood pressure, cramping, irritants

dorsal root ganglion

Visceral sensory nerves [GVA]• run with sympathetic & parasympathetic nerves• cell bodies in dorsal root ganglion• nerve ending in viscera

Visceral Afferents and Referred PainReferred Pain: • Pain originating in a visceral structure

perceived as being from an area of skin innervated by the same segmental level as the visceral afferent

• Results from convergence of somatic & visceral afferents on the same

segmental level of the spinal cord• “Cross-talk” in the dorsal horn

somatic afferent

visceral afferent

convergence &“cross-talk”

Kandel et al. 2000

www.merck.com

Grant’s Atlas 12 2009

Visceral Afferents and Referred Pain

Maps of Referred Pain

ReferencesAgur, A. M. R. and A. F. Dalley. 2009. Grant’s Atlas of Anatomy, 12th

Edition. Lippincott, Williams & Wilkins, New York.Kandel, E. R., J. H. Schwartz, and T. M. Jessell. 2000. Principles of

Neural Science, 4th Edition. McGraw-Hill, New York. Moore, K. L., A. F. Dalley and A. M. E. Agur. 2010. Clinically Oriented

Anatomy, 6th Edition. Lippincott, Williams & Wilkins, New York.Sadler, T. W. 2004. Langman’s Medical Embryology, 9th Edition.

Lippincott, Williams & Wilkins, New York.